The present invention relates to an apparatus and a method for alarming a decrease in tire air-pressure and, more particularly, to an apparatus and a method for alarming a decrease in tire air-pressure, in which an installation space can be saved and the cost of manufacturing can be reduced.
As a safety device for a four-wheeled vehicle such as a passenger car, there has been conventionally known an apparatus for alarming a decrease in tire air-pressure of a system for detecting a change in tire air-pressure based on variations in wheel speed information. Such an apparatus is configured such that a sine-wave analog signal output from a wheel speed sensor provided in each of four wheels is taken out via a special signal line, to be then captured as a pulse of a wheel speed signal through a binarization circuit, as illustrated in FIG. 5, or that a signal is directly captured from another calculator having a wheel speed signal captured therein, for example, an ABS calculator via a memory, and an alarm is issued upon detection of a decrease in tire air-pressure, as illustrated in FIG. 6.
However, the alarming apparatus, in which the signal line is used exclusively for each of the wheel speed signals, needs four pieces (or sets) of signal lines, and therefore, has been not acceptable in the current circumstance in which the cost is to be cut down by reducing the number of lines as possible.
Furthermore, the above-described alarming apparatus, in which the wheel speed signal is captured from the other calculator via the memory, need to use both of the calculator and the memory. Consequently, the alarming apparatus must be mounted on a substrate on which the calculator capturing the wheel speed signal is mounted, thereby arising a problem of severe limitation of the freedom of design for mounting the alarming apparatus and the calculator.
In the meantime, there has been known an apparatus for detecting a decrease in tire air-pressure wherein a detection signal output from the wheel speed sensor is once captured into an ABS microcomputer as the wheel speed signal binarized in the binarization circuit, and then, captured information on the number of wheel speed pulses (i.e., data on the number of pulses and a measurement time) is received via a communication line (Japanese Unexamined Patent Publication No. 71818/1998). The above-described detecting apparatus is simplified in configuration and reduced in cost by omitting an input interface circuit, which has been conventionally provided in a microcomputer for detecting a decrease in tire air-pressure.
However, the communication line in the above-described detecting apparatus connects the ABS microcomputer to the microcomputer for an apparatus for alarming a decrease in tire air-pressure in a one-to-one correspondence, and therefore, the communication line is increased in length in the case where the two microcomputers are positioned apart from each other, thereby arising problems of easy occurrence of a communication error in addition to an increase in cost, resulting in the low freedom of the layout of the microcomputer.
In view of the above-described circumstances, an object of the present invention is to provide an apparatus and a method for alarming a decrease in tire air-pressure, in which the cost of manufacturing can be reduced by using an on-vehicle communication network (hereinafter referred to as an on-vehicle LAN).